Magnetic material



June 4, 1929. G. w. ELMEN ,7 7

v MAGNETIC MATERIAL Filed June 50, 1926 6 Shets-Sheet 1 l I l I l l l ll I l 4L 8 l6 7.4 57. 4O 2 A H b Co, Ni, Fe Silicon STeel Armco \ronJ1me 4, 1929. G. w. ELMEN 1,715,647

MAGNETIC MATERIAL Filed June 30, 1926 6 Sheets-Sheet 2 Fly. 7

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MAGNETI C MATERIAL Filed June 30, 1926 6 Sheets-Sheet 4 l l I I L 1 I Ia J I 2 H5 4 v H lnrenfar: V 60.5fm W f/mefl Jame 4,-w29. ELMEN1,715,647 MAGNETIC MATERIAL I Filed June 30, 1926 e Sheets-Sheet 5 June4, 2929. G. w. ELMEN 9 MAGNET I C MATERIAL Filed June 50, 1926 6Sheets-Sheet 6 Fly; 2.?

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UNITED STATES PATENT OFFICE.

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KAGNETIC Application filed June 30,

This invention relates to magnetic materials and more especially tomagnetic alloys containing nickel, cobalt, and iron. The particularproportions of the several constituents and the methods of preparation 4of the material are set forth hereinafter.

There have hitherto been described magnetic alloys exhibiting relativelyconstant permeability over a range of magnetizing forces and alsoexhibiting relative y low hysteresis loss. Such a material is describedin French Patent No. 606,649 granted March 12, 1926. There have alsobeen known magnetic materials comprising nickel and iron and containinga very small amount of cobalt as an impurity. An example of such analloy is that described in the paper by Arnold and Elmen entitledPermalloy published in the Journal of the Franklin Institute for May,1923, volume 195, pages 621 to 632.

, The present invention relates to magnetic materials exhibitingconstancy of permeability of an entirely different order than that ofthe material described in the French patent. It relates, moreover, tocompositions in which the cobalt content is in excess of the slightamounts which ordinarily would be present as a result of using goodcommercial nickel and is sufiicient, when the alloy is given the properheat treatment, to impart thereto properties not characteristic ofpreviously-known magnetic materials.

A novel and striking property of magnetic materials in accordance withthis invention resides in their extraordinarily constant permeabilityover a considerable range of flux densities extending from zero upward.

Another important property is substantially complete absence ofhysteresis over a considerable range of flux densities from zero upward.

Another property is the relatively high initial permeability and highpermeability throughout the range of flux densities utilized in magneticmaterials for telephone, telegraph and cable circuits and apparatus.

At higher flux densities the hysteresis loss, the remanence, and .thecoercive force are low.

At still higher flux densities the hysteresis OF LEONIA, NEW JERSEY,ASSIGNOR '10 WESTERN ELECTRIC OF NEW YORK, N. Y., A CORPORATION OF NEWYORK.

MATERIAL.

1926. Serial No. 119,623.

loop widens out and assumes a peculiar form, characterized by aconstriction at the origin.

The resistivit of magnetic materials in accordance wit this inventioncompares favorably with that of other magnetic materials and can becontrolled byv varying the proportions of nickel, cobalt and iron or bythe addition of a fourth element.

The'charaeteristics of constancy of permeability and negligiblehysteresis loss which are exhibited by these new materials in the rangeof flux densities from zero to 900 c, g. S units, more or less, areimportant in signaling and other applications in which uniformity ofcharacteristics over a wide working range is demanded. The resultingadvantages of reduced energy dissipation and reduction of wavedistortion will be apparent to those skilled uin the signaling art.However, these materials exhibit many desirable properties at high fieldstrengths and hence are useful for general application aselectromagnetic materials. In particular the low hysteresis, lowremanence, low coercivity, and relatively high specific resistance arenoteworthy.

A particular magnetic material in accordance with the invention consistsof approximately 45% nickel, 25% cobalt and 30% iron with about .572, ofmanganese added to ,increase the workability. This material may be potannealed and cooled slowly in the furnace in accordance with the firstheat treatment hereinafter specified. It has a facecentered cubiccrystalline structure. The curves given in Figs. 1 to 9, inclusive,relate to a specimen of this particular composition but are illustrativeof the properties of other compositions within the scope of theinvention.

Someof the properties of this particular this material as compared withhysteresis Y loops for Armco iron and silicon steel under force of 80gauss similar conditions, a indicating the'new material, 6 siliconsteel, and c Armco lIOIl.

Figs. 4 to 8, inclusive, show in each case half of a hysteresis loop atdifferent magnetizing forces respectively; and

Fig. 9 shows ha f of a hgsteresis loop of the material at a considera lyhigher maximum flux density than in the preceding figures.

Figs. 10 to 14, inclusive, illustrate the properties of a specimen ofmaterial of approximately 60% nickel, 15% cobalt and 25% iron; Fig. 10shows both a magnetization curve and a hysteresis loop for B=13250; Fig.11 is a graph of permeability for varying values of magnetizing force;and Figs. 12 to 14, inclusive, are halves of hysteresis loops forseveral values of induction; Figs. 13 and 14 also show the magnet- 100ization curve of the virgin material as well as the hysteresis loops.

Figs. 15 to 18, inclusive, lllustrate the properties of a composition ofapproximately 73.3% nickel, 6% cobalt, 20.5% Iron and .2% manganese;Fig. 15 1s a graph of permeability with varying values of magnetizingforce; and Figs. 16 to 18 illustrate halves of hysteresis loops forseveral values of induction.

Figs. 19 to 22, inclusive, relate to a material comprising approximately50% nlckel, 30% cobalt and 20% iron; Fig. 19 1s a graph of permeabilityfor varying values of magnetizing force; and Figs. 20 to 22 are halvesof hysteresis loops for several different values of maximum induction.

Figs. 23, 24, 25, 26, 27 and 28 relate to a composition of approximately10% nickel, cobalt and 20% iron with a small fraction of 1% ofmanganese; Fig. 23 is a graph of permeability with varying values ofmagnetizing force; Fig. 24 teresis loop for an applied magnetizing andalso a magnetization curve of the virgin material which curve isdistinguished from the loop by having dots instead of circles; and Figs.25 to 28 illustrate halves of hysteresis loops for varying values ofmaximum induction.

In all the figures of the drawing which involve magnetizing forces andflux densities these quantities are plotted in c. g. s. units.

The curves of Figs. 1 and 2 indicate the remarkable constancy ofpermeability up to a magnetizing force of almost two gauss. Inaccordance with Fig. 2 the initial permeability is about 460 for thisparticular material. The curve of Fig. 1 also shows that the materialhas the high fiux densit of 15000 .c. g. s. units at a magnetizing orceof 45 gauss.

Curve 0 of Fig. 3 represents the upper shows a half hyshalf of thehysteresis loop for this alloy for flux densities up to 600 c. g. s.units represented as a straight line. By ballistic methods no hysteresisloss could be detected and the coercive force and remanence wereindicated as zero. By more accurate inductance bridge methods,applicable to low inductions, the hysteresis loss was found to be .02410" ergs per cu. cm. per cycle at an induction of 100 c. g. s. units.This value is so nearly negligible that the hysteresis loss could not berepresented on any feasible scale that could be used in the drawings andhence the hysteresis loop appears as a straight line.

The hysteresis loss in a nickel-iron alloy containing 78 nickel and 21%%iron, heat treated to develop high initial permeability, is much lessthan for silicon steel or iron. In a particular sample of such an alloy,the hysteresis loss at an induction of I c. g. s. units was found to be33 10' ergs per cu. cm. per cycle, which is over 1000 times that foundby the inductance bridge method for the specimen composed of 45% Ni, 25%Co, and 30% Fe.

Figs. 4 to 9, inclusive, illustrate half hysteresis loops of thematerial for various maximum inductions and show the manner of growth ofthe hysteresis loss with increasing induction. The curve of Fig. 4 issimilar to the curve a of Fig. 3, the circles on this graph indicatingthe ascending branch and the dots the descending branch. The dots andcircles fall on a straight line passing through the origin, indicatingthe absence of hysteresis, remanence and coercive force. The magnetizingforce and maximum induction under which this remarkable conditionprevails are the same as those for constancy of permeability. Fig. 4indicates that the magnetic material has an entirely negilgible changeof permeability up to inductions of 600 c. g. s. units.

Figs. 5 to 8, inclusive, show the growth of the hysteresis loss as theflux density increases above the highest value shown in Fig.

4. Figs. 5 and 6, for example, but the areas of the loops arecomparatively small and the hysteresis loss is not material. When theflux density reaches values of 1500 or more, as shown inFigs. 7 and 8,the hysteresis loss increases rapidly but it is to be noted that theresidual magnetization and the coercive force are still practicallyzero.

Fig. 9 shows "half of the hysteresis loop ppearance of hysteresis isevident in for a flux density of approximately 15,000 I c. g. s. units.This loop has the general shape of the ordinary hysteresis loop obtainedwith iron and other magnetic materials. It differs radically from thecurves ofi Figs. 7 and 8 in v and remanence are considerable althoughless than in most magnetic materials. This that the coercive force isparticularly true of the remanence. The hysteresis loss at this highmaximum flux density is also relatively small compared with that ofother magnetic materials.

The curves of Figs. 10 to 14, inclusive, relate to a compositionconsisting of approximately 60% nickel, cobalt and 25% iron. In thiscase the initial permeabil' ity is 631 and no change of ipermeabilityappears up to a flux density 0 700 c. g. s.

9 units.

A composition consisting of approximately 70% nickel, 15% cobalt and 15%iron has an initial permeability of 390 and no appreciable change inpermeability up to 1nduetions of 200 c. g. s. units.

The curves of Figs. 15 to 18, inclusive, relate to a compositionconsisting of approximately 73.3% nickel, 6% cobalt and 20.5% iron and.2% man anese which has an initial permeability change in permeabilityup to inductions of 715 c. g. s. units. The maximum permeability isabout 5600 at a magnetizing force of 1.1 gauss. I

A composition of approximately 20% nickel, 50% cobalt and 30% ironexhibits a negligible change of permeability at magnetizlng forces of 4gauss which produce in this instance a flux density of 450 c. g. s.

- units.

. nickel, 30% cobalt and The curves of Figs. 19 to 22, inclusive, relateto a compositionof approximately 20% iron which possesses an initialpermeability of 231 which is constant up to value of B=716 or H==3.1.

Figs. 23 to 28, inclusive, relate to a composition of 10% nickel, 70%cobalt and 20% iron which has contant permeability and zero hysteresisloss up to a flux density of 225, the permeability being 57 in thisrange.

It will be noted that the iron content.

ranges between 10% and 40% in all of these compositions. Suchcompositions have small or entirely negligible hysteresis loss forvalues of B up to 500 or 1000 as well as negligible coercive force andremanence at inductions of 500 to 1000 and very low coercive force andremanence, often approaching zero, at inductions up to 5000 c. g. s.units.

The range of proportions of the materials, nickel, cobalt and iron, maybe stated in general as follows: The magnetic material contains nickelin a substantial percentage of the total nickel, cobalt and ironcontent; cobalt in a percentage whose lower limit is a few percent, andof an upper limit of considerably more than one-half the material, andthe balance iron. For the highest values of initial permeabilitycombined with constancy of permeability experiments have indicated thatthe nickel should comprise at least 20% of the magnetic materialcontent.

I The highest degree of constancy of permeof 1430 and no appreciablebility and low hysteresis loss has been obtained with percentages ofiron ranging up to 40% although percentages of iron somewhat above 40%yield materials having to some extent the. desirable properties. hereindescribed.

In order to further illustrate the propert es of these materials thefollowing addit1onal data is given. The composition of 4 nickel, 25%cobalt, and 30% iron, hereinbefore described, has a resistivity of'19m1cro-ohm-cms.; a maximum permeability of 2075 at H=4.12; remanence of3400 and coercive force of 1.3after the application of a magnetizingforce of H=50 gauss. The hysteresis loss is negligible at a maximum fluxdensity of 570 c. g. s. units, and is 9.54 ergs per cu. cm. per cycle'at820,- 15.65 ergs at 960, 93.2 ergs at 1500, 1185 ergs at 5050, 2500 ergsat 8480, and 3375 ergs at 14900.

The material comprising 60% nickel, 15% cobalt and 25% iron has a fluxdensity of 13,250 0. g. s. units at H=30.7; a resistivity of 17.5micro-ohm-cms., remanence and coercive force of 1700 and .7 respectivelyafter an applied field of H=30.7 gauss and a maximum permeability of2680 at H=2.45. The hysteresis loss is negligible up to B=695, and is1.24 ergs per cu. cm. per cycle at a maximum flux density of 725 c. g.s. units, 8.4 ergs at 840, 27 ergs at 1050, 88 ergs at 1520, 632 ergs at5400, 1240 ergs at 8230, and 1508 ergs at 13,250. 1

The material of 73.3% nickel, 6% cobalt, 20.5% iron and 2% manganese hasa reslstivity of 15.5 micro-ohm-cms; remanence and coercive force of2700 and .35 respectively after an applied magnetizing force of H=21gauss; maximum permeability of 5600 at H=1.1 gauss; and negligiblehysteresis loss at flux densities up to 715 c. g. s. units. Thehysteresis loss per cu. cm. per cycle is 23 ergs at a flux density of1520 c. g. s. units, 348 ergs at 5125, and 783 ergs at 11,500.

The materialof 10% nickel, cobalt, and 20% iron with a fraction of 1%ofmanganesehas a resistivity of 15.36 micro-ohmcms.; remanence andcoercive force of 9340 and 3.56 after an applied magnetizing force ofgauss; maximum permeability'of 1545 at H=6.5; and negligible hysteresisloss at flux densities up to 228 c. g. s. units. The hysteresis loss peron. em. per cycle is 8 ergs at a flux density of 340 c. g. s. units, 150ergs at 620, 1040 ergs at 17 00, 2740 ergs at 3950, and 14,160 ergs at15,500 0. g. s. units.

In each case the remanence and coercive force are negligible at fluxdensities at which the permeability is constant and the hysteresis lossnegligible, and small 'at higher values of flux density. The tendency ofthe remanence and coercivity to remain small after the application ofmagnetizing forces higher than those at which the permeability remainsconstant is indicated in the drawings. For example in Fig. 8 thecoerclve force and remanence are mdicated as zero after an appliedmagnetizing force of 3.2

' increase the specific resistance of the mate- 45% nickel, 25% itssubsequent removal increases the initial rial or for other purposes.

A peculiar characteristic, often exhibited by magnetic materials inaccordance with the invention, is that the application of a directcurrent or uni-directional magnetizing force of large value and itssubsequent reduction to a low value causes the substance to have agreatly increased permeability for superimposed low alternatingmagnetizing forces. In a particular case the application of a largeuni-directional magnetizing force of about 25 gausses to the compositionof cobalt and 30% iron and permeability from 435 to 750.

In other words, the permeability curve follows the curve of Fig. 2 forincreasing applied magnetizing fields but on decreasing the field bysmall steps and remeasuring the permeability the values of permeabilitydepart from the curve of Fig. 2. This departure is not great until thepoint of maximum permeability is reached. To the left of the point ofmaximum permeability, the value of permeability, after highmagnetization, is considerably above the curve, and, in the particularcase mentioned above, had an initial value of. 750. When a specimen ofmaterial is thus highly magnetized the characteristic of constantpermeability for a range of magnetizing forces is impaired. To bring theinitial-permeability back to a lower value it is necessaryto demagnetizethe material. To restore the constancy of permeability to the fullestextent it is advisable to treatment.

Another characteristic usually exhibited by these materials is that themagnetization curve often lies partly without the hysteresis loop forhigh values of induct-ion. A

give the material a renewed heat typical case is indicated by Fig. 10where the magnetization curve (indicated by dots) is shown crossing thelower branch of the hysteresis loop (indicated by small circles) at aninduction of B=about 500 and joining it again at an induction of B=about7000.

In Fig. 13 the magnetization curve lies wholly within the hysteresisloop and in Fig. 14 is shown the case where the magnet- V ization curvecrosses and has a small portion lying without the hysteresis loop. Forall hysteresis loops of this particular specimen O. in 180 minutes formaximum inductions greater than shown in Fig. 14 the magnetization curvehas a portion lying without the hysteresis loop.

Another characteristic is that the hysteresis loss reaches a maximum ata certain value of flux density and does not increase for greater fluxdensities.

The magnetic properties of materials in accordance with this inventionare subject to change under the influence of mechanical strains andstresses and consequently due precautions must be taken in theirutilization to avoid excessive strains and stresses.

Magnetic materials, in accordance with this invention, may be preparedby melting the constituents together in an induction furnace. Goodgrades of material of commercial purity are suitable. The molten metalis cast into rods or bars. These rods or bars are worked by rolling,swaging, or drawing into desired shapes.

After the mechanical fabrication of the parts into their final'sliapesthey are heat.

treated in order to produce the desired magnetic properties. Thetemperature to which the material is heated and the rate of coolingdetermine ,very largely the relative values of the several magneticcharacteristics.

For heat treatment as hereinafter described about 40 grams of thematerial is prepared in the form of a thin tape which is rolled into afiat spiral. The thickness of the spiral i. e. the width of the tape is1/8 inch (3.175 mm.). The internal diameter ,of the spiral is 3 inches(7.62 cm.) and the external diameter 3-1/2 inches (8.89 cm.).

In accordance with a first method of preparation, the material may bepot annealed, using ordinary precautions to prevent oxidation, at about1100 C. for at least one hour, after which it is allowed to cool slowlyto room temperature in the furnace. This is the method which was used inproduction of the materials, whose magnetic characteristics are shown inFigs. 1 to 28, inclusive. In a particular instance in which this firstmethod was used the material was placed in a nichrome pot. The pot wasabout l/2 full. A rim around the potprojected above the cover. A layerofiron filings, placed on the cover, the rim. The pot was placed in anelectric furnace when its temperature was about 900 C. In 90 minutes thetemperature of the, pot rose to 1100 C. and it was maintained at thattemperature for 70 minutes. The material was then allowed to cool in thefurnace and reached a temperature of 350 of cooling time. In accordancewith a second method the pot annealed material is reheated above. themagnetic transition-temperature i. e., about 725- C. and cooled fasterthan in the first was retained by ample, by placing case, for example,at about an average rate of 2 C. to 5 0. per second down to about 350 C.and thereafter to room temperature at any desired rate.-

In accordance with a third method the ot annealed material is reheatedto about 25 C. and is cooled rapidly as, for exthe spiral of tapeweighing 40 grams on a large copper plate in the open air. The 40 gramsof material is in the form of thin tape wound into a spiral rin ofinternal diameter 3 inches (7.62 cm. external diameter 3-1/2 inches(8.89 cm.), and thickness 1/8 inch (3.175 mm.), which is the width ofthe tape.

Of these methods the first gives the -materials the most nearly constantpermeability and the lowest hysteresis loss over a wide range of fieldstrengths.

Treatment in accordance with the second method gives higherpermeability, particularly at low magnetizing forces but thepermeability is not so constant or not constant over so great a range.

The third method produces still higher permeability particularly incompositions with a high nickel content but with a greater tendency tovariations in permeability with increasing magnetizing forces andgreater tendency to increase in hysteresis loss at low field strengths.

The methods of heat treatment may be varied as experience may indicate.The particular methods given illustrate the principle that the degree inwhich the various properties are present is dependent to some extentupon the heat treatment and that various special properties may beobtained to an increased extent not only by proper selection of theproportions of the constitu cuts of the composition but also byselecting a suitable heat treatment.

Among the uses for which this material is adapted are coil or lumpedloading and continuous loading of lowand carrier frequency signalingconductors in submarine and land line telephony 'and telegraphy, loadingcoils for composite telephone and telegraph systems, repeating coils ortransformers, especially battery supply coils, wave filter coils,certain important classes of relays, dynamo-electric machinery, highfrequency electromagnetic devices, and magnetic circuits of electricalmeasuring instruments. 1 I

As an illustration of uses of magnetic ma-' terials in accordance withthe present invention in order to take advantageof the importantcharacteristic of constant pern1e ability over a range of magnetizingforces, may be mentioned its use for the continuous loading of telephoneconductors in accordance with applicants United States Patent 1,586,883granted June 1, 1926, or the continuous loading of long submarinetelegraph cables for high speed signaling in accordance with UnitedStates patent to Buckley 1,586,874 granted June 1, 1926. The use of thepresent material offers great advantages over the use of materials ofpermeability variable within the range of magnetizing forces employed.

The magnetic material of a continuously loaded conductor may be giventhe desired magnetic properties by first applying the loading materialto the conductor and then heat treating a coil of the conductor ofconsiderable radius in a suitably large furnace in accordance with themethods hereinbefore described.

What is claimed is:

1. A magnetic material including at least two magnetic elements andhaving negligible variation in permeability over a range of fluxdensities at least 50 c. g. s. units in width and lying between zero asalower limit and 5000 e. g. s. units as an upper limit.

2. A magnetic material including at least two elements of the magneticgroup having negligible hysteresis loss over a range of flux densitiesof at least 50 c. g. s. units and lying within the range employed inelectric communication circuits.

3. A magnetic material including at least two elements of the magneticgroup, having substantially constant permeability for flux densitiesbelow the general range of B=500 4. A magnetic material including atleast two elements of the magnetic group having negligible hysteresisloss for flux densities below the general range of B=500 to 1000.

5. A magnetic material comprising nickel 10% or ninre, cobalt 5% ormore, and iron in a substantial amount but not to exceed about 45%, then1ckel-cobalt-iron content being at least 85% of the total.

6. A magnetic material having a variation in permeability of less than2% over a range. of flux densities from zero to at least 50 c. g. s.units. 7

7. A magnetic material having a variation in permeability of less than2% for flux densities up to at least 600 c. g. s. units.

8. A magnetic composition having a hysteresis loss of less than .15X 10ergs per cycle per cubic centimeter for a range of magnetizing forcesfrom zero up to at least 50 c. g. s. units.

9. A magnetic-material having negligible variation in permeability overa wide range of flux densities which requires the application of areverse magnetizing force a few tenths of a c. g. s. unit or less torestore the flux to zero after the application of a magios netizingforce suflicient .to produce a value of induction up to B=5000.

10. A magneticmaterial having negligible variation in permeability werewide range of flux densities and having a residual flux of less than afew hundred c. g. s. units after the application of a magnetizing forcesufiicient to produce flux densities up to B=5000. 11. A magneticmaterial containing cobalt and having substantially constantpermeability over a range of low magnetizing forces from zero to atleast c. g. s. unit.

12. A magnetic composition comprising nickel, cobalt and iron asessential elements thereof characterized in that it forms part at leastof a magnetic circuit in inductive n relation to an electric conductor.

13. A magnetic material having negligible variation in permeability overthe general range of flux densities below B=500 to 1000 c. g. s. unitscomprising nickel, cobalt and iron.

14. A magnetic composition comprising nickel, cobalt and iron asessential constitu- 'ents thereof characterized in that the compositionhas been heat treated to give it a constant permeability over a range oflow magnetizing forces extending from zero to at least c. g. s.*unit. v

15. A magnetic composition comprising nickel, cobalt and iron asessential elements thereof characterized in that it has lower hysteresisloss at all inductions than Armco iron.

16. A magnetic composition containing nickel, cobalt and iron havingnegligible hysteresis loss for values of induction up to at least 500 c.g. s. units.

17 A magnetic composition containing nickel, cobalt and iron asessential constituents thereof having a coercive force of a few tenthsof a c. g. s. unit or less for values of induction up to a least 5000 c.g. s. units.

4 cobalt and iron having stant '65 18. A magnetic material havingnegligible variation in permeability over a wide range of fluxdensities, comprising nickel, cobalt and iron, in which a magnetizingforce of gauss induces a flux of 15,000 c. g. s. units 19. A magneticcomposition comprising nickel, cobalt and iron as essential elementsthereof characterized in that the hysteresis loss increases very rapidlyover a small range of increasing magnetizing forces whlle for smallerforces the hysteresis loss is ized in that the permeability issubstantially constant at magnetizing forces from zero to at leastaround one gauss.

21. A magnetic composition comprising as essential constituents thereofnickel,

substantially conpermeability and substantially no hysteresis,remanence, or coercivity for a 22. A magnet-ic material, comprising asessential constituents thereof nickel, cobalt and iron, havingsubstantially constant permeability at magnetizing forces from 'zeroupward to a certain value and having at larger magnetizing forces *aconsiderably higher permeability, which is retained after a very largemagnetizing force is applied and removed.

23. A magnetic material containing nickel, cobalt and iron as essentialconstituents thereof characterized in that the reversible permeabilitypossessed by the material at low unidirectional magnetizing forces isincreased to a higher value by the application and removal of a largemagnetizing force.

24. A magnetic material comprising nickel, cobalt and iron in which thecobalt content comprises approximately,10% to 35% of thenickel-cobalt-iron content.

25. A magnetic composition comprising nickel, cobalt and iron asessential elements thereof characterized in that iron constitutes aroundor less of the nickel-cobalt-iron content.

26. A magnetic composition comprising nickel, cobalt and iron asessential elements thereof characterized in that the iron comprisesaround 50% or less and the cobalt around 35% or less of thenickel-cobalt-iron composition.

27 A magnetic material comprising nickel, cobalt and iron as essentialconstituents thereof in which the nickel component comprises 9% to 81%of the nickel-cobalt-iron content.

28. A magnetic material comprising nickel, cobalt and iron as essentialconstituents thereof in which the nickel component comprises 30% to ironcontent.

29. A magnetic alloy comprising nickel between 9% and 81%, cobaltbetween 4% and 80% and iron between 5% and 45% of the entirenickel-cobalt-iron content.

30. A-magnetic alloy comprising nickel between 15% and 81%, cobaltbetween 15% and 45% and iron between 9% and 45% of the entirenickel-cobalt-iron content characterized by a permeability which variesless than 5% over a range of flux densities from zero to 500 c. g. s.units.

31. nickel, cobalt and iron in the approximate proportions of 60%, 15%and 25%, respectively.

. 32. A magnetic composition comprising nickel, cobalt and iron asessential elements thereof characterized in that it constitutes of thenickel-cobalt,

A magnetic material comprising at least part of a magnetic circuit foran electric circuit designed to operate by impressing upon thecomposition magnetizing forces of such magnitude as to produce thereinmaximum flux densities of less than 1000 c. g. s. units.

33. A magnetic composition comprising nickel, cobalt and iron asessential elements thereof characterized in that over a range of lowmagnetizing forces it has substantially constant permeability and thatit forms part at least, of a magnetic circuit upon which are to beimpressed a range of such small magnetizing forces that the permeabilityremains substantially constant.

34. A magnetic composition comprising nickel, cobalt and iron asessential elements thereof characterized in that it constitutes part atleast of a magnetic circuit in inductive relation to a signalingconductor.

35. A magnetic composition comprising nickel, cobalt and iron asessential elements thereof characterized in that it constitutes part atleast of a magnetic circuit in inductive relation to a signalingconductor in a submarine cable.

36. A magnetic composition including 45% to 75% nickel and caused tohave by the addition of suitable alloying elements and heat treatment aninitial permeability of 200 or more and a constancy of permeabilitywithin up to a magnetizing force of at least .2 c. g. 5. units.

37. A magnetic composition comprising nickel and iron in the proportionsof between 50% to 81% nickel and between 50% to 19% iron and caused tohave by the addition of suitable alloying elements and heat treatment aninitial permeability of at least 200 and constancy of permeabilitywithin 5% up to a magnetizing force of .2 c. g. s. units.

38. A magnetic material comprising nickel, cobalt and iron as essentialconstituents thereof in which the nickel component comprises 50% to(55%, the cobalt component comprises to and the iron component comprises10% to 30% of the nickelcobalt-iron content.

In witness whereof, I hereunto subscribe my name this 29th day of June,A. D. 1926.

GUSTAF W. ELMEN.

